1. Field of the Invention
The present invention relates to a preheating device of an illuminating unit for illuminating indicators and displays used for instruments for a vehicle.
2. Description of Related Art
According to Japanese Patent Laid-Open Publication No. Hei 2-80916, an illuminating unit for illuminating the instrument panel, letters and numerals by a cold cathode fluorescent lamp has been known. The instrument panel is made of a smokey light shielding film or the like except the indicating portions and the cold cathode fluorescent tube is disposed at the back of the instrument panel.
However, when such an illuminating unit is employed for instruments of a vehicle when the outside temperature is very low at a severely cold time, the temperature of the cold cathode fluorescent tube of the illuminating unit is also low, resulting in poor illuminating efficiency inside the fluorescent tube and in an insufficient brightness.
Therefore, a heater is disposed around the cold cathode fluorescent tube to heat the cold cathode fluorescent tube when the temperature is very low, thereby preventing deterioration of the brightness.
In case such an illuminating unit is employed for a vehicle, the illuminating unit is heated by the heater at a low temperature when the ignition key switch is turned on. However, a certain time is necessary until the temperature rises, a driver has to wait until a sufficient brightness is obtained.